First is to configure my server for internet access, however using a public DNS like 8.8.8.8. After DNS server is configured and tested ok, I'll change the DNS-server IP(on the DNS server) to its own server-IP.

8) CHECK DNS CONFIG FILES - if there are any issues
command: sudo named-checkconf /etc/bind/named.conf
if all is well, there shouldnt be any output - meaning configuration is ok.

9) CONFIGURE DNS-SERVER IP ON SERVER
In my case, since the DNS server-IP is the same IP-address as the server itself, I editted my /etc/network/interfaces file and changed DNS server IP as follows:
dns-nameservers (my-dns-server-ip)